1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same.
2. Description of the Related Art
As the nonvolatile memory capable of storing information even after the power supply is turned off, the flash memory and the ferroelectric memory are known.
Out of them, the flash memory has a floating gate buried in a gate insulating film of an insulated-gate field effect transistor (IGFET), and stores the information by accumulating electric charges representing the stored information in this floating gate. However, the flash memory has such a disadvantage that the memory needs a relatively high voltage because a tunnel current must be supplied to the gate insulating film in writing or erasing the information.
In contrast, the ferroelectric memory, also called FeRAM (Ferroelectric Random Access Memory), stores information by utilizing the hysteresis characteristic of the ferroelectric film formed in the ferroelectric capacitor. The ferroelectric film generates the polarization in response to the voltage applied between the upper electrode and the lower electrode of the capacitor. The spontaneous polarization still remains in the ferroelectric film after the voltage is taken away. When the polarity of the applied voltage is reversed, the spontaneous polarization is also reversed. Thus, the information can be written into the ferroelectric film by relating the direction of the spontaneous polarization with “1” and “0”. The FeRAM has such advantages that the voltage required for the writing operation is lower than the flash memory and the writing operation can be performed at a higher speed than the flash memory.
The electric characteristics of the ferroelectric capacitor that the FeRAM has depend on unevenness of an upper surface of the upper electrode, in addition to a film quality of the ferroelectric film. Therefore, it is preferable to form the upper electrode so that the upper surface of the upper electrode is planarized.
In following Patent Literatures 1 to 8, technologies related to the above FeRAM are disclosed.                [Patent Literature 1] Patent Application Publication (KOKAI) 2004-311868        [Patent Literature 2] Patent Application Publication (KOKAI) 2003-273328        [Patent Literature 3] Patent Application Publication (KOKAI) 2003-258127        [Patent Literature 4] Patent Application Publication (KOKAI) 2003-318371        [Patent Literature 5] Patent Application Publication (KOKAI) 2004-247324        [Patent Literature 6] Patent Application Publication (KOKAI) 2004-241679        [Patent Literature 7] Patent Application Publication (KOKAI) 2004-253627        [Patent Literature 8] Patent Application Publication (KOKAI) 2004-47943        